Description

This should be a really simple addition. ;)

In my app's root template I change the style according to site settings; everything's ok until the user logs out, then he gets a "completely different" site.
Of course I can fix this e.g. with a middleware, but I guess it can't hurt to populate the logout view's context in the same way as the login view's.

Many thanks to gabrielhurley for putting most of this together. Also to
bmihelac, arthurk, qingfeng, hvendelbo, petr.pulc@…, Hraban for
reports and some initial patches.

The patch also contains some whitespace/PEP8 fixes.

Backport of [13980] from trunk. Some items could be considered features
(i.e. supporting RequestSite in various contrib apps), others are definite
bugs, but it was much more robust to backport all these tightly related
changes together.